Variable resistance unit



B W. DAVID March 18, 1930.

VARIABLE RESISTANCE UNIT Filed Feb 24 w a va MM MM Patented Mar. 18,193% W. DAVID, OE CLEVELAND, OHIO, ASSIG-NOR T0 WALTER M. SCOTT, 0E

- LW'OOD, GHIO vnaraarnnnsrsrencn um'r Application filed February 24,1925. Serial No. 11,092.

This invention relates to variable resistance units and has particularreference to an improved form of potentiometer or rheostat such ascommonly used in radio circuits.

The primary object of the present invention is to provide an improvedform of variable resistance unit which shall be simple in construction,inexpensive to manufacture, and which shall be entirely enclosed andhence dust proof and eficient in operation.

Another object is to provide a resistance unit which shall include aresiliently mounted contact element which shall contact with theresistance element over a relatively large area thereby materiallyreducing the wear on the resistance element and also insure good contactat all positions.

A further object is to provide a resistance unit which shall be variablethroughout its range with a particularly smooth wiping action and evenpressure of the contact element with resistance element therebyproviding what is commonly referred to as a smooth tread.

A still further object is to provide a resistance unit of the aforesaidcharacter which may be constructed equally well as a potentiometer or arheostat and which may be easily and quickly mounted on a panel.

W'ith these and other objects in View, the

invention consists in the various novel fea tures of construction andarrangement or combination, all of which will be fully describedhereinafter and pointed out in-the appended claims. 7

In the drawing accompanying and forming a part of this application,Fig.1 is a ver tical sectional view through a rheostat constructed inaccordance with my invention and showing the same mounted on a panel;Fig. 2 is a transverse sectional view taken on the line 22 of Fig. 1;Fig. 3 is a vertical sectional view taken at right angles to that shownin Fig. 1; and Fig. 1 is a front elevation of the casing with thevariable contact finger assembly removed therefrom and show ing themanner of connecting the resistance element when used as apotentiometer.

Describing the various parts by reference about a non-conductor 6. Thisresistance ele- 6 ment may be wound with any suitable gauge resistancewire and is substantially circular in contour so that it may bepositioned within recess 2 and seated against shoulder 41. Theresistance element is prevented from rotating within the casing by theends of the insulation 6 contacting with an inwardly projecting lug 7formed within casing 1.

A metallic cap 9 normally closes the open side of casing 1 and this capis preferably fastened to the casing by drilling a series of aperturesthrough the side wall of the cap and casing and inserting thereinsuitable dowels or pins 10.

The cap 9 is provided with a central aperture 11 which is adapted toreceive a bushing 12. This bushing is formed with a reduced diameterdefining a shoulder 13 which normally contacts with the inner face ofcap 9 to prevent withdrawal of the bushing from the casing, and theouter end of the reduced portion is swaged over to fasten said bushingt0 the cap. The outer end of bushing 12 is reduced and threaded, asindicated at 14, so that this outer end may be inserted through asuitable aperture 15 in a panel 16. A nut 17 may be threaded on theouter end 14 thereby to mount the device on the panel.

A shaft 19 is rotatably-mounted within 0 bushing 12 and the inner end ofthe shaft is reduced, as indicated at 20 to receive an arm 21, the samebeing retained on the inner end of the shaft by swaging over the reducedend 20 as at 22.

@ne end of arm 21 is directed inwardly and upwardly as indicated at 23while the opposite end of said arm is directed inwardly as at 2 1. Theinwardly directed portion 2 1 is adapted to receive and support acontact element 25 which is preferably formed from relatively thinresilient metal bent substantially circular in shape and provided at oneside with an outwardly directed projection 26 which forms a contactshoe. This contact shoe is preferably formed so as to enclose theinwardly and upwardly directed end 23 of arm 21- for a purpose to bereferred to hereinafter. The ends of the contact element 25 areoverlapped and'riveted as at 27 to the inwardly directed end 24 of arm21. This arrangement provides an exceedingly resilient contact shoe andat the same time provides a construction having sufficient strength toinsure proper contact of shoe 26 with resistance element 25 at alltimes. It will be noted that the contact shoe is free to move radiallyto conform to any irregularities of the resistance element but ispositively rotated about said resistance element at diametricallyopposite points. In other words, the contact element is rotated by arm21 through the inwardly turn-ed end 24 and rivet 27 and also by theinwardly and upwardly directed end 23 which is positioned within theportion of the element refining the contact shoe 26, hence there will bea positive drive between shaft 19 and the contact element, so that thesame will rotate directly therewith and without dragging when the shaftis rotated, and at the same time the contact shoe will be free to moveradially to readily conform with the inner surface of the resistanceelement. The arm 23 also serves as a reinforcing member when the contactelement is rotated against stop lug 7 and hence prevents the resilientcontact shoe from becoming bent or jumping over the stop lug.

The reduced inner end 30 of shaft 19 is adapted to bear against aconducting spring 31 which is mounted on the inner face of the casing 1and is fastened thereto by means of a screw 32 which is threaded in abushing 33 projecting through said casing. This spring is normallyprevented from rotating about screw 32 by means of a boss 34 formedWithin the casing. One end of the resistance element 5 is connected to ascrew 35 which is threaded into a bushing 36 located diametricallyopposite bushing 33 and the outer ends of bushings 33 and 36 are adaptedto receive each a screw 37 to facilitate electrical connection of therheostat.

The outer end of shaft 19 is adapted to receive a suitable operatingknob 38 of any suitable construction which may be conveniently fastenedto the shaft 19 by means of a set screw 40. If desired, the cap 9 may beformed with a suitable number of apertures 41 so as topermit inspectionof the resistance element and interior contact assembly and it will benoted that these apertures are normally closed when the device ismounted on a panel, thereby excluding dust from the casing.

In Fig. 4 I have shown a slightly modified form of construction which isdesirable when the device is to be used as a potentiometer. In thisinstance, the casing 1 is provided with bushings 33 and 36, as before,and also with a third bushing 43. Plate 31 in this instance is fastenedto bushing 43 by means of a screw 44, and bushings 33 and 36 havefastened thereto, the two ends 45 and 46 of the resistance element 5. Athird boss 47 is formed within the casing 1 to prevent rotation ofcontact spring 31 about screw 44. In other respects the device isessentially the same as described in connection with the rheostat.

A resistance unit constructed as above described consists of few partswhich may be readily assembled and the device as a whole may be easilyand conveniently mounted upon a panel by drilling a single holetherethrough. The device is entirely enclosed so as to prevent theentrance of dust or other foreign matter which, as is well known, causessuch devices to be noisy in operation, when used in radio circuits. Thecontact shoe 26 engages 'over a broad area of the resistance elementrather than on the edge as in previous practice and hence wear due tofriction between the shoe 26 and resistance wire is reduced to aminimum.

Good electrical connection between terminal 37 and the contact shoe isinsured at all times by the pressure of spring 31 against the end 30 ofshaft 19. This particular manner of providing electrical connectionbetween the terminal and contact shoe provides an automatic takeup forany wear that might develop between the outer reduced end 30 of theshaft 19 and spring 31 which would not be the case if electricalconnection were made through bushing 12 which is the usual practice. Thedevice as a whole is normally sealed to prevent tampering although ifaccess should be desired the dowels or pins 10 may be easily drilledout, whereupon the cap 9 may be quickly removed. The terminals of thedevice are spaced relatively far apart and are surrounded entirely byinsulating material so that connection therewith may be easily madewithout danger of contact with metal parts. The bearing in the device isrelatively long due to the use of a thin flat plate for arm 21 and henceall wobbling of the shaft and contact shoe is eliminated. Having thusdescribed my invention, what I claim is:

1. A resistance unit comprising a/ casing, a resistance element carriedby said casing, a shaft, and a resilient contact element connected tosaid shaft and adapted to engage with said resistance element, saidcontact element being substantially circular in shape and provided atone side with a projection forming a shoe, a pair of binding postscarried by said casing, a conducting spring having one end secured toone of said binding posts and the opposite end bearing against saidshaft and an electrical connection between said resistance element andthe other of said binding posts.

2. In a resistance unit. of the class described, a casing having a pairof binding posts carried thereby, a shaft, an arm carried by said shaftand a contact element connected to said arm, said contact element beingsubstantially circular in shape and havin a resilient projection at oneside adapted to engage with said resistance element and a conductingspring connected at one end with one of said binding posts and havingits opposite end bearing against said shaft.

3. A resistance unit comrising a resistance element and a contactelement engaging the said resistance element, a casing enclosing saidresistance element and contact element, a shaft projecting through aWall of said cas ing and connected with said contact element, a pair ofthreaded bushings projecting through said casing, a connection betweenone of said bushings and said resistance element and a resilientconnection between the other of said bushings and said shaft and meanscarried by said casing for preventing relative movement between saidlast named connection and casing.

4. A resistance unit of the character set forth comprising a casinhaving a resistance element supported thereby, a shaft arranged withinsaid casing, an arm carried by said shaft, a contact element carried bysaid arm and being substantially circular in shape and provided with anoutwardly directed resilient portionforming a contact shoe, a stop lugon said casing for limiting the movement of said contact shoe, said armserving as a means for preventing said shoe from jumping over said stoplug.

v5. In a resistance unit of the character set forth, the combination ofa casing, a resistance element supported thereby, a shaft journaled insaid casing, an arm carried by said shaft, a resilient substantiallycircular member carried by said arm and having an outwardly directedportion surrounding one end of said arm and defining a contact shoe,said arm serving as a positive drive between said shaft and contactelement so that the same will rotate directly therewith, said contactshoe being adapted to move radially in conformity with the surface ofthe resistance element.

In testimony whereof, I hereunto aiiix my signature.

BRUCE W. DAVID.

